The present invention relates generally to an apparatus and method for inspecting a structure and, more particularly, to an apparatus and method for inspecting a structure that utilizes a driven probe proximate one surface of the structure and a tracking probe proximate the opposed surface of the structure with the driven and tracking probes being magnetically attracted to one another through the structure such that the tracking probe moves in concert with the driven probe as the driven probe is advanced over the structure.
Non-destructive inspection of structures involves thoroughly examining a structure without harming the structure or requiring significant disassembly of the structure. Non-destructive inspection is advantageous for many applications in which a thorough inspection of the exterior and/or interior of a structure is required. For example, non-destructive inspection is commonly utilized in the aircraft industry to inspect aircraft structures for any type of internal or external damage to the structure.
Among the structures that are routinely non-destructively tested are composite structures. In this regard, composite structures are commonly used throughout industry because of their engineering qualities, design flexibility and low weight. As such, it is frequently desirable to inspect composite structures to identify any flaws, such as cracks, voids or porosity, which could adversely affect the performance of the composite structure.
Various types of sensors may be utilized to perform non-destructive inspection. One or more sensors may move over the portion of the structure to be examined, and receive data regarding the structure. For example, a pulse-echo, thru-transmission, or shear wave sensor may be utilized to obtain ultrasonic data, such as thickness gauging, detection of laminar defects and porosity, and/or crack detection in the structure. Resonance, pulse echo or mechanical impedance sensors may be utilized to provide indications of voids or porosity, such as in adhesive bondlines of the structure. The data acquired by the sensors is typically processed by a processing, element, and the processed data may be presented to a user via a display.
The non-destructive inspection may be performed manually by technicians who typically move an appropriate sensor over the structure. The manual scanning generally consists of a trained technician holding a sensor and moving the sensor along the structure to ensure the sensor is capable of testing all desired portions of the structure. In many situations, the technician must repeatedly move the sensor side-to-side in one direction while simultaneously indexing the sensor in another direction. For a technician standing beside a structure, the technician may repeatedly move the sensor right and left, and back again, while indexing the sensor between each pass. In addition, because the sensors typically do not associate location information with the acquired data, the same technician who is manually scanning the structure must also watch the sensor display while scanning the structure to determine where the defects, if any, are located in the structure. The quality of the inspection, therefore, depends in large part upon the technician""s performance, not only regarding the motion of the sensor, but also the attentiveness of the technician in interpreting the displayed data. Thus, manual scanning-of structures is time-consuming, labor-intensive, and prone to human error.
Automated inspection systems have been developed to overcome the myriad of shortcomings with manual inspection techniques, but the automated systems may sometimes be too expensive, too bulky and/or require access to portions of a structure that are difficult, if not impossible, to access. For example, the AUSS system is a complex mechanical scanning system that employs through-transmission ultrasonic inspection. The AUSS system can also perform pulse echo inspections, and simultaneous dual frequency inspections. The AUSS system has robotically conrtrolled probe arms that must be positioned proximate the opposed surfaces of the structure undergoing inspection with one probe arm moving an ultrasonic transmitter along one surface of the structure, and the other probe arm correspondingly moving an ultrasonic receiver along the opposed surface of the structure. As will be apparent, conventional automated scanning systems, such as the AUSS system, therefore require access to both sides or surfaces of a structure which, at least in some circumstances, will be problematic, if not impossible. In order to maintain the ultrasonic transmitter and receiver in proper alignment and spacing with one another and with the structure undergoing inspection, the AUSS system has a complex positioning system that provides motion control in ten axes. As will be recognized, this requirement that the orientation and spacing of the ultrasonic transmitter and receiver be invariant with respect to one another and with respect to the structure undergoing inspection is especially difficult in conjunction with the inspection of curved structures.
In order to increase the rate or speed at which the inspection of a structure is conducted, the scanning system may include ultrasonic probes that have arrays of ultrasonic transmitters and receivers. As such, the inspection of the structure can proceed more rapidly and efficiently, thereby reducing the costs associated with the inspection. Unfortunately, the use of arrays of ultrasonic transmitters and receivers is generally impractical during the scanning of curved structures, such as large-scale curved composite structures. In this regard, conventional ultrasonic scanning systems for inspecting large-scale curved composite parts utilize water jets to provide water between the surface of the structure undergoing inspection and the ultrasonic transmitter or receiver in order to effectively couple ultrasonic signals into and out of the structure. In instances in which the ultrasonic probes include an array of ultrasonic transmitters or receivers, it has been difficult to design a corresponding water jet array that does not produce significant interference or crosstalk between the elements of the array.
In light of the foregoing background, an improved apparatus and method for inspecting a structure, such as a composite structure and, in particular, a curved composite structure, are provided according to the various embodiments of the present invention. Although the method and apparatus of the present invention utilize probes including respective sensing elements, such as respective ultrasonic transducers, that are disposed proximate the opposed surfaces of a structure, only one of the probes need be driven, such as by means of a robotic arm or the like. Thus, the method and apparatus of the present invention are advantageously adapted to inspect structures in which a surface of the structure is relatively inaccessible, at least for a robotic arm or the like. Additionally, embodiments of the method and apparatus of the present invention are capable of operating in an ultrasonic array mode, even in conjunction with the inspection of curved structures, thereby increasing the speed and efficiency with which such structures may be inspected and correspondingly reducing the cost associated with the inspection. Further, embodiments of the method and apparatus of the present invention permit the probes to contact and ride along the respective surfaces of the structure, thereby reducing the necessary sophistication of the motion control system that is otherwise required by conventional scanning systems in order to maintain the ultrasonic probes in a predefined orientation and at a predefined spacing from the respective surface of a structure undergoing inspection.
The apparatus of the present invention includes a driven probe disposed proximate a first surface of the structure and a tracking probe disposed proximate an opposed second surface of the structure. The driven probe is moved along the first surface of the structure in response to the application of motive force, such as by means of a robotic arm or other positioning system. In contrast, the tracking probe generally moves along the second surface of the structure in response to the movement of the driven probe and independent of the application of any other motive force. Thus, the tracking probe generally passively follows the movement of the driven probe such that the tracking probe need not be engaged by a robotic arm or other positioning system. The tracking probe can therefore be disposed on the backside or other surface of a structure that is relatively inaccessible.
To facilitate the coordinated movement of the tracking probe in conjunction with the driven probe, both the driven probe and the tracking probe advantageously include a magnet which draws the driven and tracking probes toward the first and second surfaces of the structure, respectively. Additionally, the magnetic attraction between the magnets of the driven and tracking probes causes the tracking probe to be moved over the second surface of the structure in response to corresponding movement of the driven probe.
The driven probe includes a sensing element for inspecting a structure as the driven probe is moved along the first surface of the structure. While the sensing element may be an x-ray detector, a camera or the like, the sensing element is typically an ultrasonic transducer. Typically, the tracking probe also includes a sensing element, such as an ultrasonic transducer. The ultrasonic transducers may be an ultrasonic transmitter, an ultrasonic receiver, or both.
In order to facilitate the coupling of the ultrasonic signal between the ultrasonic transducer of the driven probe and the structure, a couplant may be disposed between the ultrasonic transducers and the respective surfaces of the structure. While air or water jets may be utilized a couplant, the driven probe of one advantageous embodiment may also include an inlet for liquid that is bubbled between the ultrasonic transducer and the first surface of the structure. In this regard, the driven probe may include a housing in which the magnet and the ultrasonic transducer are disposed, and which defines the inlet. The inlet may be in fluid communication with that portion of the ultrasonic transducer that faces the first surface of the structure. Thus, the liquid bubbled between the ultrasonic transducer and the first surface of the structure facilitates coupling of the ultrasonic signals produced by the ultrasonic transducer into the structure. Likewise, the tracking probe may include an inlet for liquid that is bubbled between the ultrasonic transducer of the tracking probe and the second surface of the structure. In this regard, the tracking probe can also include a housing in which the magnet and the ultrasonic transducer are disposed, and which defines the inlet. Again, the inlet is in fluid communication with that portion of the ultrasonic transducer of the tracking probe that faces the second surface of the structure. Thus, ultrasonic signals emerging from the structure can be effectively coupled to the ultrasonic transducer of the tracking probe by the liquid bubbled therebetween. By bubbling liquid between the ultrasonic transducers and the respective surfaces of the structure, water jets are not required such that the ultrasonic transducers of the driven and tracking probes may include arrays of ultrasonic transducers, thereby permitting the rate at which the structure is inspected to be increased and the associated inspection cost accordingly decreased.
According to one advantageous embodiment, the driven probe includes at least one contact member, such as a plurality of wheels, for contacting the first surface of the structure. Thus, the driven probe may ride along the first surface of the structure. As such, the orientation of the driven probe relative to the first surface of the structure and the spacing of the driven probe relative to the first surface of the structure may be maintained by the contact between the driven probe and the first surface of the structure without requiring the complex motion control systems utilized by conventional scanning systems. Likewise, the tracking probe may include at least one contact member, such as a plurality of wheels, for contacting the second surface of the structure such that the tracking probe is also capable of riding therealong. Like the driven probe, the tracking probe may therefore be maintained in a predefined orientation and at a predefined spacing relative to the second surface of the structure without requiring the complex motion control systems utilized by conventional scanning systems. This independence from the motion control systems utilized by conventional scanning systems further reduces the cost of the apparatus of the present invention and permits the tracking probe to be moved in a controlled fashion over a surface of a structure that is relatively inaccessible for a robotic arm or other conventional motion control system. The driven and tracking probes may also utilize the water that is bubbled over the surface of the structure as a water bearing to maintain their spacing and orientation.
According to another aspect of the present invention, a method of inspecting a structure is provided. In this regard, the driven probe is positioned proximate the first surface of the structure, and the tracking probe is positioned proximate the opposed second surface of the structure. For example, driven and tracking probes may be disposed in contact with the first and second surfaces of the structure, respectively, thereby simplifying the alignment and spacing of the probes relative to the respective surfaces of the structure. The method of inspecting a structure also establishes magnetic attraction between the driven and tracking probes such that the driven and tracking probes are drawn toward the first and second surfaces of the structure, respectively. The driven probe is then moved along the first surface of the structure, such as in response to the application of a motive force by a robotic arm or other positioning system. The movement of the driven probe and the magnetic attraction between the driven and tracking probes causes the tracking probe to be correspondingly moved along the second surface of the structure. Advantageously, the tracking probe moves along the second surface of the structure independent of the application of any motive force. Thus, the tracking probe may be disposed proximate a relatively inaccessible surface of a structure since the movement of the tracking probe need not be controlled by a robotic arm or other positioning system.
As the driven probe is moved along the first surface of the structure, ultrasonic signals are transmitted to the structure by the ultrasonic transducer of one of the probes and are received by the ultrasonic transducer of the other probe following propagation through the structure. In order to effectively couple the ultrasonic signals between the driven and tracking probes and the structure, a liquid may be bubbled between the driven and tracking probes and the first and second surfaces of the structure, respectively, while ultrasonic signals are transmitted into and received from the structure. By coupling the ultrasonic signals by means of a bubbled liquid, the driven and tracking probes may include respective arrays of ultrasonic transducers in order to increase the speed with which the structure is inspected and to correspondingly decrease the cost of inspection. Alternatively, air or water jets may be utilized as the couplant.